Transmitting apparatus

ABSTRACT

A transmitting apparatus for cross connecting and transmitting main signals which enter via ring-configured transmission lines to which working and protection channels have been assigned in first and second directions, and rescuing a main signal by looping back the main signal in the opposite direction using the protection channel when a transmission line fails. Storing non-rescue information which indicates whether each channel that is the object of rescue by loop-back is a non-rescue channel. Determining whether a failure for which rescue is impossible has occurred in each channel, which is the object of rescue, other than a non-rescue channel. On the basis of main-signal cross-connect information, interchanging a result of discrimination of each channel and inserting the interchanged result of discrimination in the main signal of the corresponding channel after cross connect.

BACKGROUND OF THE INVENTION

This invention relates to a transmitting apparatus which constructs aring network that is capable of transmitting in first and seconddirections. More particularly, the invention relates to a transmittingapparatus for cross connecting and transmitting signals on respectivechannels which enter via transmission paths to which working andprotection channels have been assigned in each of the transmissiondirections, and rescuing a signal by looping back the signal in theopposite direction using the protection channel when a transmission pathfails.

Synchronous optical networks (SONET), which utilize opticalcommunication that is capable of high-capacity transmission, have becomewidespread owing to an increase in communication traffic. With SONET,user data undergoes multiplexed transmission in accordance with aSynchronous Transport Signal (STS-N) frame (where N represents aninteger) format. FIG. 12 is a diagram showing the structure of a 51.84Mbps STS-1 frame. The frame has 9×90 bytes overall (810 bytes/125 μs),of which 3×9 bytes constitute overhead OH and 87×9 bytes constitute anSTS payload STS-1 SPE (Synchronous Payload Envelope). Nine bytes of thepayload constitute path overhead PON, and VT (Virtual Tributary) packetsof V multiple channels are multiplexed onto the remaining 86×9 bytes.With SONET, frame formats other than the STS-1 frame format mentionedabove include STS-3 (155.52 Mbps), STS-12 (622.08 Mbps) and STS-48(2.488 Gbps). These frame formats can be used in appropriate fashion byoptical transmission lines.

(a) VT Structure

VT packets are of four types, namely VT 1.5, VT 2, VT 3 and VT 6, asshown (a) through (d) of FIG. 13. A VT 1.5 packet is composed of 27(=3×9) bytes, and the bit rate of ore VT channel is 1.728 Mbps (=27×8/125 Mbps). A VT 2 packet is composed of 36 (=4×9) bytes, and the bitrate of one VT channel is 2.30 Mbps (=36× 8/125 Mbps). A VT 3 packet iscomposed of 54 (=6×9) bytes, and the bit rate of one VT channel is 3.456Mbps (=54× 8/125 Mbps). A VT 6 packet is composed of 108 (=12×9) bytes,and the bit rate of one VT channel is 6.912 Mbps (=108× 8/125 Mbps).

(b) Mapping of VT 1.5 Packets into STS-1 SPE

FIG. 14 is a diagram useful in describing the mapping of VT 1.5 packetsinto a VT-structured STS-1 SPE (Synchronous Payload Envelope). A firstcolumn is for path overhead POH, and 30^(th) and 59^(th) columns are forfixed stuff composed of all “1”s. The 30^(th) and 59^(th) columns dividethe STS-1 SPE into three areas of 28 columns each. The 1^(st) to 28^(th)columns of each area are assigned 1-1, 2-1, 3-1, 4-1, 5-1, 6-1, 7-1,1-2, 2-2, . . . , 7-4 sequentially. VT 1.5 packets of the first channelare placed in the 2^(nd), 31^(st) and 60^(th) rows, VT 1.5 packets ofthe second channel are placed in the 3^(rd), 32^(nd) and 61^(th) rows,and VT 1.5 packets of the 28^(th) channel are placed in the 29^(th),58^(th) and 87^(th) rows.

A VT superframe (multiframe) having a 500-μs structure is defined byfour VT-structured STS-1 SPE frames. As shown in FIG. 15, V1, V2 bytes(VT payload pointers), a V3 byte (pointer action byte) and a V4 byte(undefined byte) are arrayed at the leading positions (2^(nd) to 29^(th)columns of the first row) of each STS-1 SPE that constructs this VTsuperframe; the remainder constitutes a VT SPE.

FIG. 16A is a diagram showing the overall structure of a VT superframe.The VT superframe is composed of the V1 to V4 bytes and 26 bytes perchannel. As shown in FIG. 16B, the VT SPE is composed of 4-byte VT pathoverhead VT POE (V5, J2, Z6 and Z7) and a VT payload of 28×4 VT ch (25bytes per channel). The V5 byte in the VT path overhead is the leadingbyte of the VT SPE and the position thereof is specified by the VTpayload pointers V1, V2. It should be noted that the V5 byte indicateserror checking, signal label and path status. It includes the parityresult of BIP-2 (Bit Interleaved Parity-2).

(c) Ring Structure

A ring structure in which a transmitting apparatus is connected in theform of a ring from the viewpoint of assuring reliability is known as anetwork configuration for SONET. The ring structure is such that if afailure occurs in a transmission path, the transmission can be continuedvia an alternative transmission path, thereby making it possible toimprove the reliability of transmission. FIG. 17 is a block diagramillustrating the structure of an ADM (Add/Drop Mux) transmittingapparatus that can be ring-connected. FIG. 18 is a diagram useful indescribing the ring structure.

The ADM transmitting apparatus is terminal equipment having a MUX(multiplexing) function and an add/drop function. More specifically, theapparatus has (1) an STS-level cross-connect function, (2) a VT-levelcross-connect function and (3) an add/drop function for the tributaryside. By way of example, line interfaces (LIF) 1 a, 1 b receive higherorder signals (e.g., OC-12 optical signals) from optical transmissionlines on EAST and WEST sides, respectively, convert these signals toelectrical signals and execute processing based upon overheadinformation. Demultiplexers (DMUX) 2 a, 2 b demultiplex higher ordersignals into lower order signals (e.g., STS-1 electrical signals), anSTS/VT cross-connect unit 3 performs switching on the STS level,multiplexers (MUX) 4 a, 4 b multiplex the switched STS-1 signals intohigher order signals and line interfaces (LIF) 5 a, 5 b add overheadonto these higher order signals, convert the signals to optical signalsand send the optical signals to the optical transmission lines on theEAST and WEST sides, respectively.

The STS/VT cross-connect unit 3 switches, on the STS level, STS-1signals inserted from tributary interfaces 6 a, 6 b, . . . via MUX/DMUXs7 a, 7 b, . . . and sends these switched signals in the EAST or WESTdirection. The STS/VT cross-connect unit 3 also drops signals, whichhave been received from the transmission line on the EAST or WEST side,on the tributary side, demultiplexes these signals to VT signals of aprescribed speed via the MUX/DMUXs 7 a, 7 b, . . . and sends the signalsto the tributary side from the tributary interfaces 6 a, 6 b, . . . .The STS/VT cross-connect unit 3 further incorporates a VT-levelcross-connect switch for separating a prescribed STS-1 signal into VTchannels, performing switching at the VT-level, multiplexing theswitched VT signals into an STS signal, subjecting the STS signal toSTS-level cross-connect processing and sending the resultant signal tothe prescribed transmission path. The transmission paths on the EAST andWEST sides both have working and protection channels assigned to them.The transmitting apparatus normally transmits signals using the workingchannel.

(d) Protection at Time of Transmission-path Failure

In accordance with the ring architecture, ADM transmitters 10 a-10 d ofthe kind depicted in FIG. 17 are connected in the form of a ring in themanner shown in FIG. 18. If a certain transmission path develops afailure or suffers a decline in quality, signals are transmitted in adirection that avoids this transmission path, thereby allowingcommunication to continue and assuring reliability and quality.

FIG. 19 is a diagram useful in describing a UPSR (Unidirectional PathSwitched Ring), which is one transmission line switching systemavailable for SONET ring networks. A transmit node A on a synchronousmultiplexed transmission line constructing the ring sends a signal intwo directions, and a receive node C selects either of these signals toeffect path switch or switch-back. In (a) of FIG. 19, the node A sendsan input signal in two directions, namely (1) a direction that leads tonode C via a node D and (2) a direction that leads to node C via a nodeB. The route that is usually selected is referred to as a “defaultpath”. If a failure develops in the transmission path from node A tonode D, as shown in (b) of FIG. 19, during communication via the defaultpath, as a result of which communication can no longer take place, nodeC selects the signal that arrives via node B, thereby allowingcommunication to continue. Such a path not selected normally but only inthe event of a failure in the default path is referred to as a“non-default path”. The functional element that performs such pathswitching is referred to as a “path protection switch”.

FIG. 20 is a diagram useful in describing rescue by a BLSR(Bidirectional Line Switched Ring) in a SONET ring network. Herecommunication is normally performed using a working channel andcommunication is rescued using a protection channel when a transmissionpath develops a failure. In case of OC-12, for example, a transmissionpath has 12 channels on the STS-1 level in the EAST and WEST directions,the first to sixth of these channels are working channels and theseventh to 12^(th) channels are protection channels. In (a) of FIG. 20,node A sends a signal, which has entered from the tributary side, tonode C on the EAST side via node D using the working channel. If thetransmission path between nodes A and D fails during this communication,node A can no longer communicate with the EAST side via node D.Accordingly, as shown in (b) of FIG. 20, the signal is sent to the WESTside over the following route: node A‡node B‡node C‡node D (the routeindicated by the dashed line), and node D effects loop-back to send thesignal to node C using the working channel. Further, in (c) of FIG. 20,node B sends a signal from the EAST side to node D via node A using theworking channel. If the transmission path between nodes A and D failsduring this communication, node A loops back the signal, which arrivesfrom node B, to the WEST side using the protection channel, and thesignal is sent to node D via nodes B and C.

(e) Transmitting Apparatus Having ADM Function

FIG. 21 illustrates a more detailed example of the structure of atransmitting apparatus equipped with the ADM function. Here thecross-connect section for performing SST cross-connect and VTcross-connect is illustrated in detail. A transmitting apparatus 10 isconstituted by an STS cross-connect unit 10A, a VT cross-connect unit20A, INF units 30 ₁-30 _(n) on the input side and INF units 40 ₁-40 _(n)on the output side.

The STS cross-connect unit 10A cross connects STS signals, the VTcross-connect unit 20A cross connects VT signals, the line INF units 30₁-30 _(n) on the input side convert optical signals, which enter fromoptical transmission paths on the EAST/WEST sides, to electrical signalsand perform STS termination processing, tributary INF units 30 ₃-30 _(n)send lower order signals, which enter from the tributary side, uponmultiplexing the signals into an STS signal, line INF units 40 ₁ ₋₄₀ ₂on the output side convert STS signals, which are output from the STScross-connect unit 10A, to optical signals and send these signals tooptical transmission paths on the EAST/WEST sides upon attachingoverhead, and tributary INF units 40 ₃-40 _(n) separate the STS signalsinto lower order signals and send these signals to the tributary side.

The STS cross-connect unit 10A has (1) STS-signal line switching units(STS TSI units) 11, 12 for performing cross-connect at the STS level;(2) an STS termination unit 14 for performing STS termination processingand separating an STS signal into VT signals; (3) an STS path protectionSW unit (STS PSW unit) 15 for performing path protection by UPSR; (4) anSTS-signal line switching unit (STS TSI unit) 13 for cross connecting,at the STS level, an STS signal obtained by multiplexing VT signalscross-connected at the VT level; and (5) a selector (SEL unit) 16 forselecting one of the STS signals cross-connected by the STS TSI unit 11and STS TSI unit 13.

The VT cross-connect unit 20A has (1) a VT SQL unit 21 for executingsquelch processing for each VT channel; (2) a VT-signal line switchingunit (VT TSI unit 22) for performing cross-connect at the VT level; and(3) a VT path protection SW unit (VT PSW unit) 23 for performing pathprotection switching. When a failure for which rescue by BLSR isimpossible occurs in a certain VT channel, squelch processing inserts anAIS (Alarm Indication Signal) (the result of squelch discrimination)into the VT channel.

Signals that have entered from the INF units 30 ₁-30 _(n) are branchedin two direction at a branch point 24 so as to enter the STA TSI units11, 12. Among the STS signals that enter from the INF units 30 ₁-30_(n), the STS TSI unit 11 cross connects, at the STS level, STS signalsthat do not require cross-connect at the VT level and inputs thesesignals to the SEL unit 16 via the STS PSW unit 15. The SEL unit 16selects the prescribed signals and inputs the selected signals to theINF units 40 ₁-40 _(n). Among the STS signals that enter from the INFunits 30 ₁-30 _(n), the STS TSI unit 12 cross connects, at the STSlevel, only STS signals that require cross-connect at the VT level. TheSTS termination unit 14 then subjects the cross-connected STS signals toSTS termination processing and inputs the obtained signal (VT signal) ofeach channel to the VT cross-connect unit 20A. The VT SQL unit 21 in theVT cross-connect unit 20A executes VT squelch processing and the VT TSIunit 22 performs cross-connect at the VT level and inputs the signals toa multiplexer (STS MUX), not shown, via the VT PSW unit 23. Themultiplexer multiplexes the VT signals into an STS signal and inputsthis signal to the STS TSI unit 13. The latter cross connects theentered STS signal at the STS level and inputs the signal to the SELunit 16. The latter selects the prescribed STS signal and inputs thissignal to the INF units 40 ₁-40 _(n). The VT SQL unit 21 executessquelch processing. When a failure for which rescue by BLSR isimpossible occurs, the VT SQL unit 21 executes squelch processing toinsert the AIS (Alarm Indication Signal) on a per-VT-channel basis.

(f) Squelch

FIGS. 22A and 22B are diagrams useful in describing VT squelch andillustrates a BLSR configuration in EAST (clockwise in FIG. 22A and WEST(counter-clockwise in FIG. 22A directions. The BLSR has a workingchannel and a protection channel in the EAST and WEST directions. FIG.22A illustrates a case where a signal (VT signal) on a prescribed VTchannel enters from a node A, passes through a node D and exits from anode B. The node ID of node B, which is the node of interest, is made 0,while the other nodes are assigned node IDs 1, 2 and 3 in ascendingorder in the WEST direction starting from 0. Each node has a squelchtable (FIG. 22B) used when determining whether to perform VT squelch(i.e., whether to insert the AIS signal). Connection-destination nodeIDs for the EAST and WEST directions are recorded in the table.Specifically, the source node of a VT signal that has been physicallyconnected to the EAST side of the node of interest is set in an EastSide column of the table, and the source node of a VT signal that hasbeen physically connected to the WEST side of the node of interest isset in a West Side column of the table. In the example of FIG. 22A, thesource node of the VT channel input and dropped on the EAST side of thenode B of interest is node A (ID=2). Accordingly, the node ID “2” is setin the East Side column of the squelch table of the above-mentioned VTchannel. Since there is no input from the WEST side, “0” is set in theWest Side column. If multiple failures occur at points E, F, node B canno longer detect the VT signal of node ID 2 as a far-end node on the VTchannel. As a result, it is judged that an unrescuable failure hasoccurred and squelch is applied to this VT channel. That is, a Path-AIS(P-AIS) is inserted into the VT signal of this VT channel.

FIG. 23 is a diagram illustrating an arrangement based upon the priorart of the VT SQL unit 21 in FIG. 21. A squelch-table setting unit 50has registers (VT1-VT28) for 28 VT channels for each of STS channels STSch1 to STS chN (50 ₁-50 _(N)). A controller (μ-COM) 57 sets data (asquelch table) in each register. SQL discrimination units 52 ₁-52 _(N)each have discriminators for 28 VT channels for each of the STSchannels, compare a far-end node ID with node IDs that have been set inthe squelch tables for each of 28×N VT channels, and determine whetherVT squelch is to be applied or not. Latches 54 ₁-54 _(N) hold theresults of discrimination for each of the 28×N VT channels, and asquelch insertion unit 56 for inserting the P-AIS into the particular VTchannel. Since the far-end node ID (the ID of the farthest node capableof data transmission among the nodes connected) is ascertained from theoverhead for every transmission path in the EAST and WEST direction, theSQL discrimination units 52 ₁-52 _(N) compare the far-end node ID withthe node IDs that have been set in the squelch tables of the VT channelsand (1) judge that an unrescuable failure has not occurred if thefar-end node ID is equal to or greater than the node ID and (2) judgethat an unrescuable failure has occurred, and insert the P-AIS into theparticular NT channel, if the far-end node ID is smaller than the nodeID. For instance, if failures occur at points E, F in the example ofFIG. 22A, the far-end node ID on the EAST side of node B is the ID “1”of node D. Since the set node ID (=2) is greater than the far-end nodeID (=1), squelch is applied to the pertinent VT channel.

(g) BLSR Information and NUT Information

Squelch inserts the P-AIS into a VT channel that cannot be rescued byBLSR (Bidirectional Line Switched Ring) loop-back. This means that it isunnecessary to apply squelch processing to a VT channel that is not theobject of BLSR rescue. In other words, squelch processing need beapplied only to a VT channel that has been mapped to an STS channelwhich is input via a BLSR; it is unnecessary to apply squelch processingto a VT channel that has been mapped to an STS channel which is inputfrom the tributary side. In the prior art, therefore, information (BLSRinformation) indicating whether a channel is the object of BLSR rescueis set for all N-number of STS channels after STS cross-connect by theSTS TSI unit 12 (see FIG. 21), and squelch processing is executed onlyfor VT channels that are the object of BLSR rescue.

Even if an STS channel is the object of BLSR rescue, this STS channelmay be one that does not use the BLSR Automatic Protection Switchtechnique. For example, there are instances where rescue by anotherrescue method such as UPSR is desired or instances where a protectionchannel is used as the equivalent of a working channel and BLSR rescueis not carried out even if a failure occurs. It is unnecessary to applysquelch processing to a VT channel that has been mapped to such an STSchannel (traffic). Such traffic is referred to NUT (Non-preemptiveUnprotected Traffic). In accordance with the prior art, therefore, NUTinformation indicating whether or not a channel is a NUT channel is setin regard to all N-number of STS channels after STS cross-connect by theSTS TSI unit 12 (see FIG. 21), and squelch processing is applied only toa VT channel of an STS channel (traffic) that is the object of BLSRrescue and that has not been set as a NUT channel. In other words, evenif a channel is one that is the object of BLSR rescue, squelchprocessing is not executed if the channel is a NUT channel.

FIG. 24 is a diagram illustrating the overall structure of a squelchprocessor having a BLSR information setting unit 61 and a NUTinformation setting unit 62. Components identical with those shown inFIG. 23 are designated by like reference characters. PS converters 53₁-53 _(N) serially convert and output the results of squelchdiscrimination of 28 VT channels stored in respective ones of latches 54₁-54 _(N), and a multiplexer 55 multiplexes N×28 results of squelchdiscrimination output from each of the PS converters 53 ₁-53 _(N) andinputs the multiplexed signal to the squelch insertion unit 56 so thatthe results of squelch discrimination are inserted into the VT-channelsignal.

The BLSR information setting unit 61 sets BLSR information in registers61 ₁-61 _(N) of respective ones of N-number of STS channels, and the NUTinformation setting unit 62 sets NUT information in registers 62 ₁-62_(N) of respective ones of N-number of STS channels. Using the BLSRinformation and NUT information regarding all STS channels, a BLSRdetermination unit 63 determines whether squelch processing is to beexecuted or not, outputs a clear signal (mask signal) CLR to thoselatches 54 ₁-54 _(N) that conform to STS channels to which squelchprocessing will not be applied, and latches the results of squelchdiscrimination only in those latches 54 ₁-54 _(N) that conform to theSTS channels that require execution of squelch processing.

(h) Activate Processing

The results of VT squelch discrimination are monitored and it isnecessary to report the squelch monitoring information to a CPU inresponse to such a request. To accomplish this, an activate processor 64is connected to the multiplexer 55, as shown in FIG. 25, and the squelchdiscrimination results of all N×28 VT channels are monitored. Theactivate processor 64 has a squelch-monitor information holding unit 64a for holding the squelch discrimination results of all N×28 VTchannels, and a timer 64 b for performing monitoring to determine, foreach of the VT channels, whether the squelch state (the unrescuablestate) has continued in excess of a set period of time. That is, asshown in FIG. 26, the activate processor 64 places informationSQL_(COM), which is shown to the CPU, at the high level when a squelchdiscrimination result SQL continues for longer than a set time ts, andplaces the information SQL_(COM) at the low level as soon as the squelchdiscrimination result SQL reverts to the low level.

FIG. 27 is a diagram illustrating the structure of the activateprocessor. The activate processor includes a storage unit 65 a forstoring squelch discrimination results (raw information) HWt of all 28×NVT channels; an EOR circuit 65 b for calculating information Δ(t, t−1)indicative of change of the raw information HWt; a latch 65 c forstoring the change information Δ(t, t−1) of all 28×N VT channels; ahardware unit 65 d for calculating and outputting information SWt, whichis seen by the CPU, in accordance with the logic table of FIG. 28; and astorage unit 65 e for storing the information SWt of all 28×N VTchannels prior to sampling.

(i) Service Selector Information

It is necessary to set whether a selector of the VT path protectionswitch unit (VT PSW 23) that follows the VT-signal line switching unit(VT TSI unit 22) (see FIG. 21) is used as a service selector or as apath selection switch of a UPSR.

FIG. 29 is a diagram useful in describing a case where the selector isused as a service selector. A BLSR ring can be expanded up to a maximumof 16 nodes. In order to accommodate a greater number of nodes, however,it is necessary to construct two or more BLSR rings and interconnectthem, as illustrated in FIG. 29. A service selector (SS) implementsrescue at the VT level at the interconnection between the ring systems.That is, the service selector (SS) of one ring performs path switchingin VT-channel units for the purpose of performing rescue at the VT levelwith regard to a signal on an insertion side dropped directly from theother ring and a signal on the through side that enters from a secondarynode within the same ring. For example, a VT signal that has been sentfrom a node A of a BLSR ring R1 enters a service selector SS2 of a BLSRring R2 via an insertion side and a through side. The service selectorSS2 normally selects the VT signal that enters from the through side andsends this signal to a node A′. If a failure in the transmission pathoccurs at point F under these conditions, the service selector SS2subsequently selects the VT signal that enters from the insertion sideand sends this signal to node A′ to continue communication.

FIG. 30 is a diagram useful in describing a case where the selector isused as the path selection switch of a UPSR. Signals 77 and 78 enter aselector 76 from the EAST (default) side and WEST (non-default) side,respectively. Under the control of a PSW controller 75, the selector 76normally selects and outputs the signal 77 on the default side. An ALMdetector 70 on the default side and an ALM detector 71 on thenon-default side detect alarms on the default and non-default sides fromthe input signals, set these alarms in an ALM register 72 and notify thePSW controller 75 of the occurrence of the alarms. Accordingly, when theALM detector 70 on the default side detects an alarm duringcommunication on the default side, the selector 76 selects the signalfrom the non-default side in response to control by the PSW controller75, thereby allowing communication to continue. If, after changeoverfrom the default path to the non-default path owing to a failure, thedefault path recovers from the failure, a switch is made back to theoriginal default path upon elapse of a time WTR (wait to Restore) thathas been set in a WTR control register 74. The WTR time is set in theWTR control register 74 by a CPU 73.

FIG. 31 is a diagram showing an arrangement in which a service selectorinformation setting unit 66 is on the output side of the squelchprocessor. Components in FIG. 31 identical with those shown in FIG. 24are designated by like reference characters. The VT-signal lineswitching unit (VT TSI) 22 and VT path protection SW unit (VT PSW) 23are connected to the squelch insertion unit 56 successively in the ordermentioned. The selector of the VT path protection SW unit (VT PSW) 23sets, for all N×28 VT channels, whether the selector of the VT pathprotection switch unit (VT PSW) 23 is used as a service selector or as apath selection switch of a UPSR. A P/S converter 67 reads out the setservice selector information successively in sync with the VT channelsand inputs this information to the VT path protection SW unit (VT PSW)23. The latter executes a selection operation as a service selector oras a UPSR path switch based upon the service selector information.

(j) Synchronous Control between Two VT Switches

In order to make possible the co-existence of VT switching and ATMswitching, there is an ATM apparatus having two slots for VT and ATMswitching and it is possible to use VT and ATM switches interchangeably.The reason for such an apparatus is that there are users who wish toperform switching at the ATM level, users who wish to perform switchingat the VT level and users who wish to perform switching at both the ATMand VT levels. In order to perform VT-level switching, it is necessaryto insert a VT switching package in each slot and pass respectivelyassigned VT channel signals (VT signals) between the two VT switches.This makes it necessary to accommodate for a phase difference between VTsignals in the two VT switches.

FIG. 32 is a diagram showing an arrangement in which VT channel signals(VT signals) are passed between VT switches 81 and 82. STS signalsoutput from an STS switch (STS TSI) 80 enter the VT switches 81, 82 onehalf at a time (DATA 1, DATA 2). The VT switches 81, 82, which areidentical in structure, have pointer replacement units 81 a, 82 a,elastic memories (ES units) 81 b, 82 b, VT line switching units 81 c, 82c, PSW/SS units 81 d, 82 d, and multiframe timing generators 81 e, 82 e,respectively. The elastic memories 81 b, 82 b, which are provided infront of the VT line switching units 81 c, 82 c, respectively,accommodate for a phase difference between the data of the two VTswitches 81, 82. VT channel signals following VT pointer replacement aresent and received between the two VT switches 81, 82, the exchanged datais stored in the elastic memories (ES units) 81 b, 82 b and the data isthen read out of the elastic memories (ES units) 81 b, 82 b at themultiframe timing, whereby accommodation is made for the phasedifference between the data of the two VT switches 81, 82.

(k) Problems to be Solved by the Present Invention

First problem

With the conventional ADM apparatus, the NUT information settingregisters 62 ₁-62 _(N), the number of which is equivalent to the number(N) of STS-1 channels, are provided as shown in FIG. 24 in order to setthe NUT information. However, unless STS signals of all N channels enterfrom the BLSR, i.e., unless all N channels are channels that are theobject of BLSR rescue, some registers will be provided needlessly. Theresult is an inefficient circuit architecture. For example, in a casewhere the ADM apparatus is capable of cross connecting STS-1 signals ofa maximum of N (=192) channels, it will suffice to provide NUTinformation for 96 STS-1 channels if the maximum transmission rate inthe EAST and WEST directions of the BLSR is OC-48; N (=192) registersneed not be provided.

Further, with regard to the setting as to whether a channel is a NUTchannel in the prior art, four types of channels, namely a workingchannel on the EAST side, a protection channel on the EAST side, aworking channel on the WEST side and a protection channel on the WESTside, will have been set up as one set in the interface on the lineside. If the transmission rate is OC-48, however, the NUT informationthat has been set for working channels #1-#24 of STS-1 on the EAST sidewill be identical with. NUT information set for protection channels#24-#48 on the EAST side, working channels #1-#24 on the WEST side andprotection channels #25-48 on the WEST side. Accordingly, it willsuffice to set NUT information only for 24 (= 96/4) EAST-side workingchannels. In a case where enhance NUT is supported (enhance NUT is NUTthat makes it possible to designate a working channel and a protectionchannel individually), the information is the same as the NUTinformation that is set for the working/protection channels in the EASTdirection and for the working/protection channels in the WEST direction.Accordingly, NUT information need be set for only 48 (= 96/2) EAST-sideworking channels and EAST-side protection channels. Nevertheless, inaccordance with the prior art, the STS signals after the cross-connectare not linked to the STS signals in the interface on the line side, andtherefore NUT information is set individually for all channels (192) ofthe four types. The efficiency of such a circuit arrangement is notgood.

Second problem

In order to identify an STS-1 channel that is the object of BLSR rescue,the BLSR information setting registers 61 ₁-61 _(N), the number of whichis equivalent to the maximum number (N) of STS-1 channels of theapparatus, are provided as shown in FIG. 24. However, BLSR informationis information that is uniquely decided line by line in the interface onthe line side of the apparatus. Providing BLSR information for everySTS-1 channel after the cross connect in STS units means that needlessregisters are provided, resulting in an inefficient architecture. Forexample, if the maximum number of STS-1 channels that can beaccommodated by a BLSR is n (OC-n), it will suffice to providen/2-number of BLSR information setting registers in common for each ofthe EAST/WEST directions and working/protection. In case of OC-48, only24 registers need be provided.

Further, according to the prior art, as shown in FIG. 24, BLSRdetermination circuits 63 ₁-63 _(N) for performing a logic operationbetween BLSR information and NUT information in order to identify BLSRtraffic, and mask processing circuits (latch circuits) 54 ₁-54 _(N) forapplying mask processing to the results of VT squelch discriminationusing this BLSR determination information, are each required to beprovided for the maximum number (N) of STS-1 channels of the apparatus.The result is an inefficient circuit arrangement.

Third problem

In order to notify the CPU of the VT squelch monitoring information,squelch monitoring information holding units are required in a numberequivalent to the number of VT channels (N×28 channels) corresponding tothe maximum VT access processing capacity of the apparatus. However,unless STS signals of all N channels enter from the BLSR, i.e., unlessall N channels are channels that are the object of BLSR rescue, someregisters will be provided needlessly. The result is an inefficientcircuit architecture. Further, even if all STS signals enter from theBLSR, needless squelch monitoring information holding unitscorresponding to protection channels that are not the object of squelchinsertion are provided. The result is an inefficient arrangement.

Fourth problem

In the prior art, whether the VT path protection switch unit (VT PSW) isto be operated as (1) a VT service selector or (2) a UPSR path selectionswitch is set by the service selector information (SS information). Morespecifically, SS information setting registers for each of N×28 VTchannels, which is the maximum VT access processing capacity, isprovided in the SS information setting unit 66 (FIG. 31) and the SSinformation of the prescribed VT channel is set in each register. The SSinformation is read out of the SS information setting unit 66 seriallyin conformity with the serial processing of the main signal and isdelivered to the VT path protection switch unit. As a result, the VTpath protection switch unit operates as a VT service selector or USPRpath selection switch based upon the SS information for each VT channel.

The VT path protection switch unit (VT PSW) operates as a VT serviceselector only with regard to VT channels accommodated by an STS-1channel that is the object of BLSR rescue. It will suffice if the VTpath protection switch unit operates as a UPSR path selection switchwith regard to VT channels other than these. This means that the SSinformation can be determined from the BLSR information and NUTinformation. Nevertheless, the prior art is such that since the VT pathprotection switch unit is situated after a VT line switching unit, SSinformation setting registers are provided individually irrespective ofthe setting of the NUT information and BLSR information. Such redundantprovision of registers results in circuitry that is not efficient.

Fifth problem

In order to make it possible for VT switching and ATM switching toco-exist, the ADM apparatus is provided with two slots for VT/ATMswitches and it is so arranged that a VT switch and ATM switch can beinterchanged. If only VT switching is performed in such an ADMapparatus, it is required that the assigned VT channel signals (VTsignals) be passed between these VT switches, as shown in FIG. 32. Forthis reason, a phase difference between the data of the two VT switchesis accommodated for by sending and receiving data, following VT pointerreplacement, between the two VT switches, storing the data in an elasticmemory provided at a position ahead of the line switching unit andreading out the data in sync with multiframe timing. However, since eachVT switch performs VT pointer replacement based upon an independentmultiframe timing, the phase difference between the data of the two VTswitches after VT pointer replacement increases. This makes it necessaryto provide an elastic memory of greater capacity in order to accommodatefor this phase difference. The result is an inefficient circuitarrangement.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a morecompact apparatus by reducing the number of registers for setting NUTinformation.

Another object of the present invention is to provide a more compactapparatus by reducing the number of registers for setting BLSRinformation, the number of BLSR determination circuits and the number ofmask processing circuits for VT squelch.

Another object of the present invention is to provide a more compactapparatus by reducing the number of channels necessary for activateprocessing, thereby reducing the number of registers for holding squelchmonitoring information.

Another object of the present invention is to provide a more compactapparatus by reducing the number of existing service selector settingregisters.

Another object of the present invention is to eliminate an elasticmemory, which is for absorbing a phase difference between VT signals ofVT switches and storing the VT signals, in a transmitting apparatus inwhich VT channel signals (VT signals) are passed between two VTswitches.

Let a direction in which a signal is input to the EAST side and outputfrom the WEST side of each node be a first direction, let a direction inwhich a signal is input to the WEST side and output from the EAST sideof each node be a second direction, and let the maximum number of STS-1channels that can be accommodated by a BLSR be n.

According to the present invention, NUT information setting registersfor n/4-number of channels, i.e., NUT information setting registers onlyfor working channels in the first direction, are provided, and NUTinformation for the working channels in the first direction is set inthese registers. The NUT information is shared as NUT information of (1)the working channel in the first direction, (2) the protection channelin the first direction, (3) the working channel in the second directionand (4) the protection channel in the second direction. In a case whereenhance NUT is supported, NUT information setting registers only forn/2-number of channels, i.e., for the working channel in the firstdirection and the protection channel in the first direction, areprovided, the NUT information for the working channel in the firstdirection and the NUT information for the protection channel in thefirst direction is set in these registers, the NUT information for theworking channel in the first direction is shared as NUT information forthe working channels in the first and second directions, and the NUTinformation for the protection channel in the first direction is sharedas NUT information for the protection channels in the first and seconddirections. If this arrangement is adopted, the size of the apparatuscan be reduced by reducing the number of registers for setting the NUTinformation.

According to the present invention, determination of channels that arethe object of squelch is performed using NUT information of STS channelsaccommodated by the BLSR and BLSR-type setting information thatindicates the BLSR transmission rate (STS-12, STS-48, etc.). If thisarrangement is adopted, the number of registers for setting BLSRinformation can be reduced, the number of channels requiring BLSRdetermination processing is diminished, thereby making it possible toreduce the number of BLSR determination circuits and mask processingcircuit for VT squelch. This results in a more compact apparatus.

According to the present invention, activate processing is applied to VTsquelch discrimination results of VT channels accommodated by an STSchannel that is the object of BLSR rescue, and the results of VT squelchdiscrimination after activation are cross connected and reported to aCPU on a per-STS-channel basis utilizing STS line setting information(STS cross-connect information) of the main signals. If this arrangementis adopted, it will suffice to hold only squelch monitoring informationfor the number of STS-1 channels accommodated by the BLSR. This makes itpossible to reduce the number of activate processing channels and,hence, to reduce the size of the apparatus.

According to the present invention, channel-by-channel BLSRdetermination results for use in squelch masking are cross connectedbased upon STS line setting information (STS-cross connect information)and VT line setting information (VT cross-connect information) of themain signals, thereby generating SS information that indicates whether aVT path protection switch is to be operated as a VT service selector. Ifthis arrangement is adopted, existing service selector setting registerscan be eliminated, thereby making it possible to reduce the size of theapparatus.

According to the present invention, multiframe timings in two VTswitches are made to coincide and VT pointers are replaced at each VTswitch using this multiframe timing as a reference, thereby minimizingthe phase difference between the data of the two VT switches. If thisarrangement is adopted, it is unnecessary to provide an elastic memoryfor absorbing the phase difference between the data of two VT switches,thereby enabling the apparatus to be made more compact.

According to the present invention, one VT switch serving as a masterdelivers a pulse BMFT, which indicates the timing of a referencemultiframe, to the other VT switch serving as a slave in order to makethe multiframe timing positions agree in the two VT switches. The pulseBMFT indicative of the timing of the reference multiframe is a timingpulse of 50% duty indicating a position one-half frame ahead of amultiframe timing pulse MF1 in the master VT switch. The slave VT switchaccepts the reference multiframe timing pulse BMFT of 50% duty,implements the prescribed protection and generates a multiframe timingpulse MF2 using, as the multiframe timing, the position of a frametiming pulse F2, which is generated within the slave VT switch, thatfirst arrives from the position of the above-mentioned multiframe timingpulse. If this arrangement is adopted, it is possible to make themultiframe timings coincide reliably without the influence of one-shotnoise.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are diagrams illustrating the overall structure of an ADMapparatus according to the present invention;

FIG. 2 is a block diagram illustrating components associated withsquelch processing;

FIGS. 3A and 3B are diagrams useful in describing the relationshipbetween BLSR types and slots;

FIG. 4 is a diagram useful in describing the correspondence between NUTinformation and NUT channels;

FIG. 5 shows an example of the setting of NUT information;

FIG. 6 shows an example of the setting of BLSR type;

FIGS. 7A to 7C are tables illustrating examples in which the scale ofcircuitry according to the present invention is compared with that ofthe prior-art apparatus;

FIG. 8 is a block diagram of an arrangement in which an activateprocessor is connected to a VT SQL controller according to the presentinvention;

FIG. 9 is a block diagram in which an SS information generator isconnected to a BLSR rescue channel discriminator;

FIG. 10 is a block diagram of double VT switches according to thepresent invention;

FIG. 11 is a time chart of various timing pulses;

FIG. 12 shows an STS-1 frame format according to the prior art;

FIG. 13 shows various VT structures according to the prior art;

FIG. 14 shows the structure of an STS-1 SPE according to the prior art;

FIG. 15 shows the structure of an STS-1 SPE of a 500-μs superframeaccording to the prior art;

FIGS. 16A and 16B illustrate the structure of a superframe according tothe prior art;

FIG. 17 is a simplified block diagram of an ADM apparatus according tothe prior art;

FIG. 18 is a diagram showing the structure of a ring according to theprior art;

FIG. 19 is a diagram useful in describing a UPSR in a SONET according tothe prior art;

FIG. 20 is a diagram useful in describing a BLSR in a SONET according tothe prior art;

FIG. 21 is a block diagram showing the system configuration of atransmitting apparatus according to the prior art;

FIGS. 22A and 22B are diagrams useful in describing the concept of VTsquelch according to the prior art;

FIG. 23 is a block diagram showing a VT squelch processor according tothe prior art;

FIG. 24 is a block diagram illustrating the entirety of a squelchprocessor having a BLSR information setting unit and a NUT informationsetting unit according to the prior art;

FIG. 25 is a block diagram of an arrangement in which an activateprocessor is connected to a squelch processor according to the priorart;

FIG. 26 is a diagram useful in describing a squelch monitor according tothe prior art;

FIG. 27 illustrates an activate processor according to the prior art;

FIG. 28 is a diagram useful in describing logical operations performedby hardware according to the prior art;

FIG. 29 is a diagram useful in describing a case where a selector of aVT-PSW is used as a service selector SS according to the prior art;

FIG. 30 is a diagram useful in describing a case where a selector of aVT-PSW is used as a path selection switch of a USPR according to theprior art;

FIG. 31 is a block diagram in which a service selector informationsetting unit is placed on the output side of a squelch processingaccording to the prior art; and

FIG. 32 is a block diagram of an arrangement in which VT signals areinterchanged between VT switches according to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT (A) ADM Apparatus According tothe Present Invention

(a) Structure

FIGS. 1A to 1C are diagrams illustrating the overall structure of atransmitting apparatus (VT cross-connect apparatus) having an ADMfunction according to the present invention. The apparatus isconstituted by an STS cross-connect unit 100, a VT cross-connect unit200, an INF unit 300 on the input side and an INF unit 400 on the outputside.

The STS cross-connect unit 100 cross connects STS signals, and the VTcross-connect unit 200 executes squelch processing and cross connects VTsignals. Line terminators 300 ₁-300 ₂ on the input side convert opticalsignals, which enter from optical transmission lines 500 ₁, 500 ₂ on theEAST/WEST sides of the ring structure, to electrical signals and performSTS termination processing, and tributary INF units 300 ₃-300 _(n) sendlower order signals such as DS1, which enter from the tributary side,upon multiplexing the VT signals into an STS signal. A SONET/SDHtransport unit 400 ₁ on the output side converts an STS signal, whichenters from the STS cross-connect unit 100, to an optical signal,attaches overhead to the optical signal and then sends the signal to anoptical transmission line on the EAST/WEST side. An STM accommodatingunit 400 ₂ decomposes an STM signal into VT signals, makes these lowerorder signals such as DS1 and sends these signals to the tributary side.

The STS cross-connect unit 100 includes (1) STS-signal line switchingunits 111, 112 for performing cross-connect at the STS level; (2) an STSpath terminating unit 113 for performing STS termination processing andseparating an STS signal into VT signals; (3) an STS path protectionswitch 114 for performing STS path protection; (4) an STS multiplexer(STS MUX) 115 for multiplexing, into an STS signal, VT signals crossconnected at the VT level; (5) an STS-signal line switching unit 116 forcross connecting, at the STS level, the STS signal output from the STSmultiplexer 115; and (6) and a selector (SEL unit) 117 for selecting oneof the STS signals cross connected by the STS-signal line switching unit111 and STS-signal line switching unit 116.

The VT cross-connect unit 200 includes (1) a VT SQL controller 211 forcontrolling VT squelch; (2) a VT SQL insertion unit 212 for insertingthe result of squelch; (3) a VT-signal line switching unit 213 forperforming cross-connect in VT-channel units, i.e., at the VT level; (4)a VT path protection switch 214 for acting as a VT service selector oras a path protection switch based upon UPSR; (5) an STS cross-connectinformation holding unit (ACM1) 215 for holding line switchinginformation (STS cross-connect information) on the STS level of the mainsignal; (6) a VT cross-connect information holding unit (ACM2) 216 forholding line switching information (VT cross-connect information) on theVT level of the main signal; (7) a BLSR rescue channel discriminator 217for discriminating, from NUT information and BLSR information, a VTchannel that is to be rescued by a BSLR, and for outputting this VTchannel; (8) a VT squelch monitor/notification unit 218 for monitoringthe results of VT squelch discrimination and reporting this to a CPU inresponse to a request; and (9) an SS information generator 219 forgenerating, on the basis of the BLSR rescue channel information(information representing the results of BLSR determination), SSinformation as to whether the VT path protection switch 214 is used as aservice selector. Let a direction in which a signal is input to the EASTside and output from the WEST side of each node be a first direction andlet a direction in which a signal is input to the WEST side and outputfrom the EAST side of each node be a second direction.

The VT SQL controller 211 includes a squelch-table setting unit 221 forsetting a squelch table for each VT channel accommodated in each STSworking channel in the first direction of the BLSR; a squelchdiscrimination unit 222 for performing squelch discrimination for eachVT channel accommodated in each STS working channel in the firstdirection; a latch 223 for latching the results of squelch on aper-VT-channel basis; a P/S unit 224 for serially outputting the squelchresults of VT channels from the latch 223 while subjecting these resultsto a parallel-to-serial conversion; and a selector 225 which, inaccordance with STS cross-connect information (line switchinginformation) of the main-signal data, interchanges the squelch resultsat the STS level and inputs the results to the VT SQL insertion unit212.

The BLSR rescue channel discriminator 217 includes a NUT informationsetting register 231 in which is set NUT information indicating whethereach STS working channel in the first direction of the BLSR is a NUTchannel; a BLSR-type setting unit 232 for setting BLSR type, whichindicates the BLSR transmission rate (OC-12, OC-48, etc.); and a BLSRdetermination unit 233 for determining, on the basis of NUT informationand BLSR type, an STS channel (BLSR rescue channel) to be rescued by theBLSR, and outputting the channel to the VT SQL controller 211 and SSinformation generator 219. The latch 223 of the VT SQL controller 211stores the results of squelch discrimination of the BLSR rescue channel(the STS channel that is the object of squelch discrimination) andmasks, and does not store, the results of squelch discrimination of anSTS channel that does not require rescue.

The VT squelch monitor/notification unit 218 includes an activateprocessor 241 which, before the results of squelch discrimination of aBLSR rescue channel are interchanged based upon STS line settinginformation (STS cross-connect information) of the main-signal data,executes activate processing with regard to these squelch discriminationresults; a selector 242 which, based upon STS line setting informationof main-signal data, interchanges and outputs the results of squelchdiscrimination following activate processing; and a μ-COM INF unit 243which executes interface processing for sending the CPU the results ofsquelch discrimination following interchange.

The SS information generator 219 includes a selector 251 which, on thebasis of the STS line setting information (STS cross-connectinformation) of the main-signal data, interchanges the results of BLSRdetermination (information indicating whether an STS-1 channelaccommodated by the BLSR is rescued by the BLSR) output from the BLSRdetermination unit 233 of the BLSR rescue channel discriminator 217; anda selector 252 for interchanging VT channels, which are accommodated byeach BLSR rescue channel interchanged, based upon line switchinginformation (VT cross-connect information) at the VT level, andinstructing the VT path protection switch 214 to act as a serviceselector with respect to the VT channels after interchange.

(b) Operation

The line terminators 300 ₁-300 ₂ and tributary terminators 300 ₃-300_(n) line- or path-terminate the signals sent from the line side andsubscriber side, branch the signals after termination and deliver themto the STS-signal line switching units 111, 112.

Among the STS signals that arrive from the line side and subscriberside, the STS-signal line switching unit 111 selects STS signals thatare allowed to pass through (STS signals that do not requirecross-connect at the VT level) and performs line switching. The STS pathprotection switch 114 operates as a path protection switch in order toperform signal rescue at the STS level.

From STS signals that arrive from the line side and subscriber side, theSTS-signal line switching unit 112 arbitrarily selects STS signals(VT-accessed STSs) that will be cross connected at the VT level. Theselection of the VT-accessed STSs is executed in accordance withselection information from the STS cross-connect information holdingunit (ACM1) 215. The STS path terminating unit 113 subjects STS signalsthat have been selected as VT-accessed STSs to STS path terminationprocessing and decomposes the signals into VT signals. The squelchinsertion unit 212 inserts VT squelch (results of squelchdiscrimination) into the particular VT channel. The VT-signal lineswitching unit 213 performs line switching in units of VT channels inaccordance with VT line setting information from the VT cross-connectinformation holding unit (ACM2) 216, and the VT path protection switch214 acts as a VT-signal path protection switch or as a service selectorswitch. The STS multiplexer (STS MUX unit) 115 multiplexes theVT-processed VT signals into an STS signal and inputs the STS signal tothe STS-signal line switching unit 116. The latter performs STS-levelline switching again.

The selector 117 selects whether the STS signal on the STS pass-throughside or the signal on the side of the VT-accessed STSs is to be outputfrom the apparatus. The selected signal is output via either theSONET/SDH transport unit 400 ₁ or STM accommodating unit 400 ₂, to theline side and subscriber (tributary) side.

The squelch-table setting unit 221 in the VT SQL controller 211 stores asquelch table, which has been set up in advance, from a CPU or the like.Using the set squelch table and the far-end node ID sent from anotherapparatus on the network at the time of failure, the squelchdiscrimination unit 222 determines whether squelch will be applied. Thelatch 223 holds the results of discrimination by the squelchdiscrimination unit 222, the P/S unit 224 reads out the latched SQLdiscrimination result information serially in STS-channel units, and theselector 225 selects the SQL discrimination result information inaccordance with the STS line setting information (STS cross-connectinformation) from the STS cross-connect information holding unit (ACM1)215 and links this information to the VT channel of the main signal.

The NUT information setting register 231 stores NUT information, whichhas been set in advance, from a CPU or the like, the BLSR-type settingunit 232 stores BLSR-type information, which indicates the set BLSRtransmission rate, from a CPU or the like, and the BLSR determinationunit 233 uses the set NUT information and BLSR-type information todetermine whether the traffic is BLSR traffic (a channel that is theobject of BLSR rescue). The NUT information setting unit 231 and theBLSR determination unit 233 are provided solely for the number of STSworking channels in the first direction assigned to the BLSRtransmission line. The result of BLSR determination are input to thelatch 223 of the VT SQL controller 211 and is used as VT-squelch maskinformation.

The selector 251 of the SS information generator 219 selects and outputseach result of BLSR determination at a timing in accordance with the STSline setting information being held by the STS cross-connect informationholding unit (ACM1) 215. As a result, STS-level channel interchange ofthe results of BLSR determination is performed and informationindicative of the results is linked to the VT channel of the main signalafter line switching at the VT level. This BLSR determination resultinformation after interchange is delivered to the VT path protectionswitch 214. The latter uses the entered BLSR determination result asservice selector information, operates as a service selector switch withrespect to the VT channel that is BLSR traffic (the channel that is theobject of BLSR rescue), and operates as a UPSR path selection switchwith respect to other traffic.

(B) Squelch Processing

FIG. 2 is a block diagram illustrating components associated withsquelch processing. Components in FIG. 2 identical with those shown inFIG. 1 are designated by like reference characters.

The type of BLSR connected to an ADM apparatus is decided in advance.For example, (1) an OC-48 BLSR ring, (2) an OC-12 BLSR ring #1 and (3)an OC-12 BLSR ring #2 are connectable to the ADM apparatus. The slotinto which the BLSR of each type is inserted into the ADM apparatus isdecided in advance. (1) In case of OC-12 BLSR ring #1, slot 1 is on theEAST side and slot 2 is on the WEST side, as illustrated in FIG. 3A; (2)in case of OC-12 BLSR ring #2, slot 9 is on the EAST side and slot 16 ison the WEST side; (3) in case of the OC-48 BLSR ring, slots 1, 9 are onthe EAST side and slots 2, 16 are on the WEST side, as shown in FIG. 3B.

If an STS channel accommodated by the OC-48 or OC-12 BLSR ring (namely achannel that is the object of rescue) is not a NUT channel, then thechannel is a channel rescued by the BLSR. In case of OC-48, STS-1 #1 to#24 on the EAST side (first direction) are working channels, STS-1 #25to #48 on the EAST side (first direction) are protection channels, STS-1#1 to #24 on the WEST side (second direction) are working channels andSTS-1 #25 to #48 on the WEST side (second direction) are protectionchannels. If STS-1 #1 to #3 on the EAST side are set as NUT channels bythe NUT information, as shown in FIG. 4, then STS-1 #25 to #27 on theEAST side and STS-1 #1 to #3, STS-1 #25 to #27 on the WEST side alsobecome NUT channels. Though the foregoing is the case for OC-48, thesame will hold also in the case of OC-12.

Thus, if the BLSR type is OC-12 ring #1 or OC-12 ring #2, it willsuffice to set NUT information for the working channels STS-1 #1 to #6on the EAST side. If the BLSR type is an OC-48 ring, it will suffice toset NUT information for the working channels STS-1 #1 to #24 on the EASTside. To accomplish this, the NUT information setting register 231 inFIG. 2 is provided with registers for setting a total of 36 items of NUTinformation and sets NUT information of working channels #1 to #6 on theEAST side of OC-12 ring #1, NUT information of working channels #1 to #6on the EAST side of OC-12 ring #2 and NUT information of workingchannels #1 to #24 on the EAST side of the OC-48 ring. In actuality,four 16-bit registers are provided, as shown in FIG. 5 (shown as D15-0),and NUT information of each BLSR type is set in respective ones of theseregisters.

Further, BLSR type (OC-12 ring #1, OC-12 ring #2, OC-48 ring) is set inthe BLSR-type setting unit 232. FIG. 6 shows an example of the settingof BLSR type. Here BLSR type is set by three bits. The OC-48 ring is setby “001”, OC-12 ring #1 is set by “010”, and OC-12 ring #2 is set by“100”. It should be noted that BLSR type can be set using two bits aswell.

The BLSR determination unit 233 decides the BLSR rescue channel basedupon the BLSR type and NUT information, inputs the BLSR rescue channelinformation (BLSR determination results) to a 36-to-24 converter 234,and the latter outputs 24 results of BLSR determination. There are threeBLSR types, namely OC-12 ring #1, OC-12 ring #2 and the OC-48 ring. Themaximum number of STS-1 channels that are the object of rescue is 24.For this reason the 36-to-24 converter 234 outputs the 24 results ofBLSR determination.

STS channels that are the object of squelch processing are channels(channels that are the object of BLSR rescue) that are not NUT channelsamong the STS channels (channels that are the object of BLSR rescue)accommodated by the BLSR. The maximum number of these STS channels is24. Accordingly, the squelch-table setting unit 221 has squelch tables221 ₁-221 _(M) (M=24) each for dealing with VT channels VT1-VT28 of eachof the STS channels ch1-ch24. The squelch-table setting unit 221records, from μ-COM, connection-destination information(connection-destination node IDs on the EAST and WEST sides) of VTchannels corresponding to each of the tables. It should be noted thatthe STS channels ch1-ch24 in the squelch-table setting unit 221 arechannels before the channels that are the object of BLSR rescue arecross connected by the STS-signal line switching unit 112.

SQL discrimination units 222 ₁-222 _(M) (M=24) each have discriminatorsfor 28 VT channels, compare, for each of 28×M VT channels, a far-endnode ID with node IDs that have been set in the squelch tables, anddetermine whether VT squelch is to be applied or not. Latches 223 ₁-223_(M) latch the results of discrimination of BLSR rescue channels basedupon the results of BLSR discrimination. The squelch discriminationresults of channels other than those that are the object of rescue aremasked and not latched. P/S converters 224 ₁-224 _(M) each seriallyconvert and output squelch discrimination results of 28 VT channelsstored in respective ones of latches 223 ₁-223 _(M). On the basis of STScross-connect information that has been stored in the STS cross-connectinformation holding unit (ACM1) 215, the selector 225 selects, inregular order, the squelch discrimination results output serially fromthe P/S converters 224 ₁-224 _(M) and inputs the results to the squelchinsertion unit 212 at the timing of the working/protection channels onthe EAST side and the working/protection channels on the WEST side. Thesquelch insertion unit 212 inserts the entered results of squelchdiscrimination into the VT signals of the applicable working/protectionchannels on the EAST side and the working/protection channels on theWEST side.

In summary, data which enters from the upper left of FIG. 2 is a signalthat is the result of decomposing, into VT signals, STS signals thathave been selected as VT-accessed STSs, and results of VT squelchdiscrimination are inserted into the applicable VT channels by thesquelch insertion unit 212.

The squelch-table setting unit 221 stores set squelch tables from a CPUor the like, and the squelch discrimination unit 222 uses a set squelchtable and a far-end node ID sent from another apparatus on the networkat the time of failure to determine whether squelch will be applied. Thelatch 223 latches the results of discrimination performed by the squelchdiscrimination unit 222. The latched information is output from the P/Sunit 224 serially STS by STS, and the selector 225 selects informationin accordance with line setting information from the STS cross-connectinformation holding unit (ACM1) 215. The squelch insertion unit 212inserts the results of squelch discrimination, which is sent from theselector 225, into main signals of the corresponding VT channels.

The NUT information setting register 231 stores set NUT information froma CPU or the like. The NUT information is prepared only for workingchannels on the EAST side used by the BLSR. In FIG. 2, NUT informationfor [six channels for OC-12 BLSR]×[24 channels for OC-48 BLSR] isprovided as an example in an apparatus corresponding to an OC-48 BLSRarrangement or OC-12 BLSR×2 arrangement.

The BLSR-type setting unit 232 stores BLSR-type information, whichindicates the set BLSR transmission rate from a CPU or the like, and theBLSR determination unit 233 uses the set NUT information and BLSR-typeinformation to determine whether the channel corresponding to theworking channel on the EAST side is actually BLSR traffic (a channelthat is the object of BLSR rescue). Since results of BLSR determinationexist for both an OC-48 BLSR and an OC-12 BLSR, either one is selectedin the 36-to-24 converter 234 based upon the BLSR-type information andthe results of VT squelch discrimination are delivered to the latch 223for the purpose of mask processing.

Thus, in accordance with the present invention, NUT informationregisters need be provided only for EAST-side working channels used bythe BLSR. This makes it possible to reduce the number of registers forsetting NUT information, to reduce the amount of circuitry and toalleviate the processing load on the CPU. If the maximum VT accessprocessing capability of the apparatus is 10 Gbps (=192 STS-1 channels),a comparison of the number (N) of NUT information setting registers inthe prior art and number (M) of registers in the present invention willbe as indicated in FIG. 7A.

Further, in accordance with the present invention, BLSR determinationcan be carried out using NUT information linked to channels (channelsthat are the object of BLSR rescue) accommodated by the BLSR andBLSR-type setting information indicative of the BLSR transmission rate.This makes it possible to reduce the number of registers for setting theBLSR. In addition, the number of channels for BLSR determinationprocessing can be reduced and it is possible to reduce BLSRdetermination circuitry and mask processing circuitry for VT squelch. Ifthe maximum VT access processing capability of the apparatus is 10 Gbps(=192 STS-1 channels), a comparison of the number (N) of BLSRinformation setting registers in the prior art and number (L) ofBLSR-type registers in the present invention will be as indicated inFIG. 7B. In addition, according to the present invention, it is possibleto reduce the number of SQL activate processing channels. In thecomparison example shown in FIG. 7C, if the maximum VT access processingcapability of the apparatus is 10 Gbps, a comparison of the number ofSQL activate processing channels (N×VT) in the prior art and the numberof SQL activate processing channels (M×VT) in the present invention willbe as indicated in FIG. 7C.

(C) VT Squelch Monitor and Notification Processing

FIG. 8 is a block diagram of an arrangement in which a VT squelchmonitor/notification unit is connected to a VT SQL controller accordingto the present invention. Components in FIG. 8 identical with thoseshown in FIGS. 1 and 2 are designated by like reference characters.

In an ADM apparatus, the results of squelch discrimination are monitoredand a report is made to the CPU in response to a request. Before theresults of squelch discrimination are interchanged based upon theSTS-line setting information (STS cross-connect information) of themain-signal data, therefore, the results are input from the P/S unit 224to the VT squelch monitor/notification unit 218, where squelch resultsconcerning BLSR rescue channels are monitored.

The VT squelch monitor/notification unit 218 includes the activateprocessor 241 for executing activate processing based upon the squelchdiscrimination results; the selector 242 for interchanging, on the basisof STS-line setting information of the main-signal data, the squelchdiscrimination results after the activate processing; and the μ-COM INFunit 243, which executes interface processing to send the CPU thesquelch discrimination results after the interchange thereof.

The activate processor 241 includes a squelch monitor informationholding unit 241 a for holding the results of squelch discrimination forall VT channels (M×28, where M=24) of channels that are the object ofBLSR rescue, and an activate timer 241 b for monitoring whether thesquelch state (the unrescuable state) has continued in excess of a setperiod of time with regard to all M×28 VT channels. The operation of theactivate processor 241 is the same as that of the prior-art exampleshown in FIGS. 26 to 28. The difference is that if the number of STSchannels that can be processed by the ADM apparatus is N (=192), theactivate processing in the prior-art example monitors squelch resultsfor all N×28 VT channels, whereas in the present invention it sufficesto monitor squelch results for M×28 VT channels if the number ofchannels that are the object of BLSR rescue is M (=24).

The activate processor 241 executes activate processing to monitor, byan activate timer, the continuity of SQL discrimination results in eachVT channel read out of the P/S unit 224 serially in STS units. Theresults of squelch discrimination of M×28 VT channels in the M-number ofchannels that are the object of BLSR rescue become the object ofactivate processing, and the squelch monitor information holding unit241 a and activate timer 241 b are prepared for M×28 channels. FIG. 8takes VT 1.5 as an example and illustrates a case where 28 VT channelsare linked to the STS-1 channel.

On the basis of STS-line setting information of the main-signal data,the selector 242 selects, in regular order, M×28 SQL discriminationresults after execution of activate processing and outputs the resultsat the timing of the working/protection channels on the EAST side andworking/protection channels on the WEST side. As a result, STS-levelchannel interchange of SQL discrimination results following activateprocessing is carried out, and the μ-COM INF unit 243 reports thesquelch-monitor information appropriately following interchange inresponse to a request from the CPU.

Thus, in accordance with the present invention, activate processing isapplied, prior to cross connect, to M×28 VT squelch discriminationresults in channels that are the object of BLSR rescue, M×28 VT squelchdiscrimination results following activate processing are interchangedutilizing the STS-line setting information of the main signals and theresults are reported to the CPU. As a result, it is possible to reducethe number of active processing channels. For example, if the maximum VTaccess processing capability of the apparatus is 10 Gbps (=192 STS-1channels), a comparison of the number (N×VT) of activate processingchannels in the prior art and number (M×VT) of processing channels inthe present invention will be as indicated in FIG. 7C.

(D) Control for Generating SS Information

FIG. 9 is a block diagram in which the SS information generator 219 ofthe present invention is connected to the BLSR rescue channeldiscriminator 217. Components in FIG. 9 identical with those shown inFIGS. 1 and 2 are designated by like reference characters.

It is necessary to set whether a selector (not shown) contained in theVT path protection switch 214 that follows the VT-signal line switchingunit 213 is to operate as a service selector or as a USPR path selectionswitch. To achieve this, it will suffice to make a setting such that theselector will operate as a service selector with respect to VT channelsaccommodated by BLSR rescue channels and as a USPR path selection switchwith respect to other VT channels.

Accordingly, the SS information generator 219 of the present inventiongenerates SS information (service selector information) using BLSRdetermination information that specifies BLSR rescue channels, and theVT path protection switch 214 is set by this SS information so that theselector will operate as a VT service selector or as a USPR pathselection switch.

The SS information generator 219 has the selector 251 which, on thebasis of the STS line setting information (STS cross-connectinformation) of the main-signal data, interchanges the results of BLSRdetermination (information indicating whether an STS-1 channelaccommodated by the BLSR is rescued by the BLSR) output from the BLSRrescue channel discriminator 217; and the selector 252 for interchangingVT channels, which are accommodated by each BLSR rescue channelinterchanged, based upon line switching information (VT cross-connectinformation) at the VT level, and instructing the VT path protectionswitch 214 to act as a service selector with respect to the VT channelsafter interchange.

The selector 251 selects and outputs the result of BLSR determination ofeach STS channel at a timing in accordance with the STS cross-connectinformation being held by the STS cross-connect information holding unit(ACM1) 215. As a result, STS-level channel interchange of the results ofBLSR determination is performed and the information is linked to the VTchannel of the main signal after STS channel switching. The selector 252further selects and outputs the BLSR determination results, which havebeen linked to the VT channel at a timing in accordance with the VTcross-connect information that has been stored in the VT cross-connectinformation holding unit (ACM2) 216. Accordingly, VT-level channelinterchange of the BLSR determination results is performed and theresults are linked to the VT channel of the main signal after the lineswitching at the VT level. The information representing the results ofBLSR determination after interchange is delivered to the VT pathprotection switch 214. The latter uses the entered BLSR determinationresult as VT service selector information, operates as a serviceselector switch with respect to the VT channel that is BLSR traffic (thechannel that is the object of BLSR rescue), and operates as a UPSR pathselection switch with respect to other traffic.

Thus, in accordance with the present invention, it is possible to reducethe number of registers (namely for N×28 channels) required in the priorart to set whether the VT path protection switch is to operate as a VTservice selector. This makes it possible to reduce the amount ofcircuitry and to lighten the processing load on the CPU.

(E) Control of Phase Difference between VT Switches

In order to make possible the co-existence of VT switching and ATMswitching, there is an ATM apparatus having two slots for VT and ATMswitching and it is possible to use VT and ATM switches interchangeably.In a case where only VT switching is performed by such an ADM apparatus,a VT switching package is inserted into each slot and VT-channel signals(VT signals) are interchanged between two VT switches. In order tointerchange the VT signals, it is necessary to accommodate for the phasedifference between the VT signals in the two VT switches.

FIG. 10 is a block diagram of double VT switches of the presentinvention equipped with an arrangement which accommodates for phasedifference. The VT switches 300, 400 have substantially the samestructures. In the present invention, VT multiframe timings in the twoVT switches 300, 400 are made to coincide and VT pointers are replacedat each VT switch using this multiframe timing as a reference. As aresult, the phase difference between the data of the two VT switches300, 400 can be minimized.

Further, in order to bring the multiframe timing positions in the two VTswitches into agreement in accordance with the present invention, one VTswitch 300 serving as a master delivers a pulse, which indicates thetiming of a reference multiframe, to the other VT 400 switch serving asa slave. This reference multiframe timing pulse is a timing pulse of 50%duty indicating a position one-half frame (=62.5 μs) ahead of multiframetiming pulse in the master VT switch 300. The slave VT switch 400accepts this reference multiframe timing pulse of 50% duty, to whichprotection has been applied, as its reference timing. As a result, it ispossible to bring multiframe timings into agreement reliably without theinfluence of one-shot noise.

In FIG. 10, a reference timing pulse that enters from the right side isa reference timing pulse having a period of 125 μs distributed from anSTS switch.

ES units (elastic memories) 301, 401 change over the reference timingpulse, which has been distributed from the STS switch, to a 78-MHzmaster clock pulse within the VT switch. Frame timing generators 302,402 executes three-stage protection, of a period of 125 μs, with regardto the frame timing after the pulse has been changed over to the masterclock pulse, and subsequently activate frame timing counters (not shown)based upon this frame timing to generate frame timing pulses F1, F2 (seeFIG. 11), which have a period of 125 μs, within the VT switches. Amultiframe timing generator 303 in the master VT switch 300 generates amultiframe timing pulse MF1 (the period of which is 500 μs) by afree-running counter based upon the frame timing pulse F1 generated inthe VT switch 300. The multiframe timing generator 303 thenceforthoutputs, to the slave VT switch 400, a reference timing pulse BMFT (theperiod of which is 500 μs) of 50% duty indicating a position one-halfframe (=62.5 μs) ahead of the multiframe timing pulse. The multiframetiming generator 303 outputs also a clock that is synchronized to thepulse BMFT.

The slave VT switch 400 has a protection unit 404 for sampling, at aperiod of 0.1 μs, the reference multiframe timing pulse BMFT (the dutyand period of which are 50% and 500 μs, respectively) that has enteredfrom the master VT switch 300, and for monitoring the continuity of thesampled values (i.e., whether three successive sampled values are at thehigh level). The protection unit 404 accepts the reference multiframetiming pulse BMFT only if the value is the same three times insuccession.

Using as a reference the reference multiframe timing pulse BMFT that hasbeen accepted from the master VT switch 300, the multiframe generator403 generates, a multiframe timing MF2 at the position of the frametiming pulse F2, which is firstly generated by the frame generator 402in this VT switch after the reference multiframe timing pulse BMFTgenerates. If this arrangement is adopted, the positions of themultiframe timings MF1, MF2 in the two VT switches will coincide.

Meanwhile, data that enters from the upper left of FIG. 10 is an STSsignal having a maximum capacity of 10 Gbps (for 192 STS-1 channels)selected as VT-accessed STSs in the STS switch (not shown) of thepreceding stage. This 10-Gbps signal has a form obtained by the16-channel multiplexing of an STS-12 signal, for example. The 16channels of STS-12 are split into eight channels each and eight channelsare input to the VT switch 300 and eight channels to the VT switch 400.

An STS bus terminator 305 (405) within the VT switch subjects the inputSTS signal of maximum capacity 5 Gbps to STS bus termination processingto decompose the signal into STS-SPE signals. A VT pointer receiver 306(406) extracts the received VT pointer values from the STS-SPE signalsand decomposes them into VT signals. Using the multiframe timing as areference, a VT pointer replacing unit 307 (407) replaces the pointervalues in order to align the V5-bit positions of the received VTsignals.

The VT signals following pointer replacement are delivered to a VT lineswitching unit 308 (408) in this VT switch and to a VT line switchingunit 408 (308) in the other VT switch. In order to reduce the number ofinterface signals, the signal that will be output from this other VTswitch 400 (300) is multiplexed into the STS-12-signal format by an STSMUX 309 (409), after which the signal is output. The other VT switch 400(300) that receives this STS signal uses an STS DMUX 410 (310) todemultiplex the STS-12 signal into VT signals, after which the VTsignals are input to the VT line switching unit 408 (308).

A PSW trigger alarm detector 311 (411) detects a VT-level alarm ALM,which is a trigger alarm of the VT path protection switch or VT serviceselector switch. An LOP-V/AIS-V detector 312 (412) detects LOP-V andAIS-V. The detected trigger alarm information and LOP-V or AIS-Vdetection information is delivered to the VT line switching unit 308(408) in this VT switch and to the VT line switching unit 408 (308) inthe other VT switch.

The VT line switching unit 308 (408) executes line switching at the VTlevel with regard to the VT signals, trigger alarm information and LOP-Vor AIS-V detection information generated in this VT switch 300 (400),and with regard to the VT signals, trigger alarm information and LOP-Vor AIS-V detection information sent from the other VT switch 400 (300).More specifically, 5376 (=192×28) VT channel signals, which are obtainedby combining the capacity of 5 Gbps processed by this VT switch 300(400) and the capacity of 5 Gbps processed by the other VT switch 400(300), are cross connected at the VT level and 2688 VT channel signalsare output.

After interchange of VT lines, a PSW or SS unit 313 (413) executes a VTpath protection switch operation or VT service selector switch operationwith respect to the VT signals and LOP-V or AIS detection information inaccordance with the trigger alarm information.

A POH insertion unit 314 (414) inserts POH information into the STS pathoverhead byte when VT signals are mapped into an STS signal. The POHinsertion unit 314 (414) has a PDI-P transmitter 315 (415) having afunction for inserting a PDI-P code into the C2 byte. The PDI-Ptransmitter 315 (415) counts the number of failed channels of VT signalsmapped into the STS signal and inserts the PDI-P code into the C2 byteof the STS signal. The calculation of the number of failed channels isperformed by counting up the LOP-V or AIS-V information.

An STS MUX 316 (416) inserts section-overhead/line-overhead informationinto the section/line overhead byte of the STS signal. The STS signal issent from the STG MUS in the STS-12 format.

Thus, the VT multiframe timings in two VT switches are made to coincideand VT pointer replacement is performed by each VT switch using themultiframe timing as a reference. This minimizes the phase differencebetween the data of the two VT switches. As a result, an elastic memorynecessary in the prior art for the purpose of storing VT signals can beeliminated. Further, by strictly discriminating reference multiframetiming pulses that enter from the master VT switch, multiframe timingscan be made to coincide reliably, without the influence of noise, in themaster/slave VT switches.

In accordance with the present invention, NUT information registers needbe provided only for STS working channels in a first direction used by aBLSR. As a result, the number of registers for setting the NUTinformation can be reduced, the amount of circuitry can be reduced andthe processing load on the CPU can be alleviated.

Further, in accordance with the present invention, BLSR determinationcan be carried out using NUT information linked to channels (channelsthat are the object of BLSR rescue) accommodated by a BLSR and BLSR-typesetting information indicative of the BLSR transmission rate. This makesit possible to reduce the number of registers for setting the BLSR. Inaddition, the number of channels for BLSR determination processing canbe reduced and it is possible to reduce BLSR determination circuitry andmask processing circuitry for VT squelch.

Further, in accordance with the present invention, the results of VTsquelch discrimination of channels that are the object of BLSR rescueare subjected to activate processing before cross connect is performed,VT squelch discrimination results following activate processing areinterchanged utilizing the STS cross-connect information of the mainsignals and the results are reported to the CPU. As a result, it ispossible to reduce the number of active processing channels.

Further, in accordance with the present invention, the results of BLSRdetermination indicative of BLSR rescue channels are interchangedutilizing cross-connect information (STS and VT) of main-signal data,and these results are delivered to a VT path protection switching unit.As a result, SS information setting registers (N×VT channel's worth) canbe reduced and it is possible to reduce the amount of circuitry and tolighten the CPU processing load.

Further, in accordance with the present invention, the VT multiframetimings in two VT switches are made to coincide and VT pointerreplacement is performed in each of the VT switches using the multiframetiming as a reference. As a result, the phase difference between thedata of the two VT switches can be minimized (an accommodation is madefor the phase difference) and the elastic memory required in the priorart can be eliminated. Further, in accordance with the presentinvention, it is possible to make the multiframe timings of two VTswitches coincide reliably without the influence of one-shot noise.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

1. A transmitting apparatus which constructs a ring network capable oftransmitting in first and second directions via first and secondtransmission lines respectively, said transmitting apparatus crossconnecting and transmitting main signals on respective channels, whichenter via one of the first and second transmission lines to whichworking and protection channels have been assigned, and rescuing a mainsignal when a transmission line fails by looping back the main signal inthe opposite direction using the protection channel of anothertransmission line, said apparatus comprising: a squelch controller fordetermining whether failure for which rescue is impossible has occurredin each channel of a second group, wherein channels that are the objectof rescue by loop-back are classified to a first group of channels whichare set so as not to be rescued by loop-back and a second group ofchannels other than the first group of channels and a channel of thefirst group is referred to as an non-rescue channel; a NUT table settingregister for storing non-rescue information which indicates whether achannel that is the object of rescue by loop-back is a non-rescuechannel; and a squelch insertion unit which, on the basis of main-signalcross-connect information, interchanges a result of discrimination ofeach channel of the second group and inserts the interchanged result ofdiscrimination in the main signal of the corresponding channel aftercross connect.
 2. The apparatus according to claim 1, furthercomprising: BLSR-type setting unit for storing ring type which specifiestransmission rate of ring network to which the transmitting apparatus isconnected; and BLSR determination circuit for deciding, on the basis ofthe ring-type information and non-rescue information, whether eachchannel that is the object of rescue is the channel of the second group;wherein said NUT table setting register has a storage area for storing,on a per-ring-type basis, non-rescue information which specifies whethera channel that is the object of rescue is a non-rescue channel; and saidBLSR determination circuit makes the decision based upon the non-rescueinformation of the ring type stored in the BLSR-type setting unit. 3.The apparatus according to claim 2, wherein said NUT table settingregister stores the non-rescue information only for working channels ina prescribed direction among the channels that are the object of rescue;said BLSR determination circuit decides channels of the second groupfrom among the working channels of said direction; said squelchcontroller determines whether an unrescuable failure has occurred in thechannel of the second group; and on the basis of main-signalcross-connect information, said squelch insertion unit interchanges theresult of discrimination of the channels of the second group and insertsthe interchanged result of discrimination in the main signal of thecorresponding channel after cross connect, this insertion beingperformed in the working channels and protection channels of the firstand second directions.
 4. The apparatus according to claim 1, whereinthe channels are STS channels in a synchronous optical network; saidsquelch controller determines whether failure for which rescue byloop-back is impossible has occurred in each virtual tributary channel(VT channel) accommodated by an STS channel of the second group; and onthe basis of main-signal STS cross-connect information, said squelchinsertion unit interchanges a result of discrimination of said each VTchannel on a per-STS-channel basis and inserts the interchanged resultof discrimination in a corresponding VT signal after STS cross connect.5. The apparatus according to claim 1, further comprising: activateprocessing means for receiving the discrimination result before it isinterchanged based upon the cross-connect information, monitoringwhether an unrescuable failure has continued in excess of apredetermined period of time for every channel, and monitoring whether arecovery from failure has been accomplished; and interchanging means forinterchanging and outputting result of monitoring on the basis ofmain-signal cross-connect information.
 6. The apparatus according toclaim 5, wherein the channels are STS channels in a synchronous opticalnetwork; said squelch controller determines whether failure for whichrescue by loop-back is impossible has occurred in each virtual tributarychannel (VT channel) accommodated by an STS channel of the second group;said activate processing means monitors whether an unrescuable failurehas continued in excess of a predetermined period of time for every VTchannel and monitors whether a recovery from failure has beenaccomplished for every TV channel; and said interchanging meansinterchanges and outputs result of monitoring of every VT channel on aper-STS-channel basis on the basis of main-signal cross-connectinformation.
 7. The apparatus according to claim 4, further comprising:a VT path protection switch having, for every VT channel, a serviceselector switch function which, when a failure has occurred in a firsttransmission path of first and second transmission paths connecting tworing networks, performs rescue by selecting a signal that enters fromthe second transmission path; and a service selector informationgenerator for generating service selector information which specifiesthat the VT path protection switch is to operate as service selectorswitch; wherein on the basis of main-signal cross-connect information,said service selector information generator interchanges informationindicating whether a channel that is the object of rescue is the channelof the second group, generates service selector information for every VTchannel by this interchange, and delivers the service selectorinformation to said VT path protection switch.
 8. The apparatusaccording to claim 7, wherein on the basis of main-signal STScross-connect information, said service selector information generatorinterchanges information indicating whether a channel that is the objectof rescue in STS working channel of a prescribed direction is thechannel of the second group, and interchanges this interchangedinformation concerning the channel of the second group on the basis ofmain-signal VT cross-connect information, thereby generating serviceselector information for every VT channel.
 9. A transmitting apparatushaving an STS switch for cross connecting an STS signal whichaccommodates a plurality of virtual tributary signals (VT signals), andtwo VT switches to which an STS signal, which has been cross connectedby the STS switch, is input upon being split into respective halves,wherein said VT switches replace VT pointers contained in the STSsignal, VT-channel signals following the replacement of the VT pointersare passed between said VT switches and the VT signals are then crossconnected, said apparatus comprising: timing adjustment unit foradjusting multiframe timing; a VT pointer replacement unit for replacingVT pointers using as a reference the multiframe timing that has beenadjusted; means for passing VT-channel signals between said VT switchesafter replacement of the VT pointers; and a VT line switching unit forcross connecting the VT channel signals.
 10. The apparatus according toclaim 9, wherein said timing adjustment unit, which is provided in oneof said VT switches (a master switch), has (1) a multiframe timinggenerator for generating a multiframe timing pulse from a frame timingpulse, and (2) a timing pulse generator for generating a referencemultiframe timing pulse of a prescribed width indicating a positionone-half frame ahead of the multiframe timing; and said timingadjustment unit, which is provided in the other of said VT switches (aslave switch), has (1) a judgment circuit for sampling referencemultiframe timing pulses at high speed and, if a sampled value of apulse has the same level a plurality of times in succession, judgingthat the pulse is true reference multiframe timing pulse, and (2) amultiframe timing generator for adopting, as a multiframe timing pulse,a frame timing pulse of the slave switch generated the first timingdetection of said reference multiframe timing pulse.